Liquid crystal compounds

ABSTRACT

A compound of formula (I): where R 1  is alkyl or alkenyl, Y 1  and Y 2  are independently selected from oxygen or sulphur, n is an integer of from 1 to 5, A is an optionally substituted phenyl or an optionally substituted cycloalkyl ring, X is a direct bond, a C 1-4 alkylene, a C 2-4 alkenylene, an acetylene, —CO(O)— or a group of sub-formula (i): where X 1  and X 2  are independently selected from a direct bond, a C 1-4 alkylene, a C 2-4 alkenylene, an acetylene, —CO(O)— and R 2 , R 3  and R 4  are independently selected from hydrogen, halo or cyano, provided that no more than one of R 2 , R 3  and R 4  is hydrogen. These compounds have a high dipole moment and may be used as dopants in liquid crystal mixtures.

This application is a 371 of PCT International application No.PCT/GB03/00305, filed 27 Jan. 2003, which designated the US and claimspriority to GB Application No. 0202201.0, filed 31 Jan. 2002. The entirecontents of these applications are incorporated herein by reference.

The present invention relates to novel compounds, which have theproperties of liquid crystals together with processes for theirpreparation and liquid crystal devices incorporating them.

The term “liquid crystals” is well known. It refers to compounds which,as a result of their structure, will align themselves in a similarorientation, preferably at working temperatures, for example of from −40to 200° C. These materials are useful in various devices, in particularthe liquid crystal display devices or LCDs.

Liquid crystals can exist in various phases. In essence there are threedifferent classes of liquid crystalline material, each possessing acharacteristic molecular arrangement. These classes are nematic, chiralnematic (cholesteric) and smectic.

Broadly speaking, the molecules of nematic compounds will alignthemselves in a particular orientation in a bulk material. Smecticmaterials, in addition to being orientated in a similar way, will alignthemselves closely in layers.

A wide range of smectic phases exists, for example smectic A and smecticC. In the former, the molecules are aligned perpendicularly to a base orsupport, whilst in the latter, molecules may be inclined to the support.Some liquid crystal materials possess a number of liquid crystal phaseson varying the temperature. Others have just one phase. For example, aliquid crystal material may show the following phases on being cooledfrom the isotropic phase: —isotropic—nematic—smectic A—smectic C—solid.If a material is described as being smectic A then it means that thematerial possesses a smectic A phase over a useful working temperaturerange.

Such materials are useful, in particular in display devices where theirability to align themselves and to change their alignment under theinfluence of voltage, is used to impact on the path of polarised light,thus giving rise to liquid crystal displays. These are widely used indevices such as watches, calculators, display boards or hoardings,computer screens, in particular laptop computer screens etc. Theproperties of the compounds which impact on the speed with which thecompounds respond to voltage charges include molecule size, viscosity(Δn), dipole moments (Δε), conductivity etc.

A number of previous patents and applications such as EP-A-0047453, EP0731155, EP-A-0385471 and U.S. Pat. No. 4,707,296 have described liquidcrystal compounds which include an alkoxyalkoxy group at one end of themolecule.

The applicants have found that a combination of an alkoxyalkoxy group atone end of a molecule, and a highly polar multiply-substituted ring atthe other end of the molecule gives a particularly good dipole moment,which may be particularly useful in certain liquid crystal devices.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing the switching behavior of Mixture 2 (seeTables 3 and 4) measured as light transmission through cell versusvoltage applied to cell; and

FIG. 2 is a graph showing the switching behavior of Mixture 3 (seeTables 3 and 5) measured as light transmission through cell versusvoltage applied to cell.

DESCRIPTION OF THE INVENTION

According to the present invention there is provided a compound offormula (I)

where R¹ is alkyl or alkenyl, Y¹ and Y² are independently selected fromoxygen or sulphur, n is an integer of from 1 to 5, A is an optionallysubstituted phenyl or an optionally substituted cycloalkyl ring, X is adirect bond, a C₂ or C₄alkylene, a C₂ or C₄alkenylene, an acetylene,—CO(O)—, or a group of sub-formula (i)

where X¹ and X² are independently selected from a direct bond, aC₁₋₄alkylene, a C₂₋₄alkenylene, an acetylene or —CO(O)—and R², R³ and R⁴are independently selected from hydrogen, halogen or cyano, providedthat no more than one of R², R³ and R⁴ is hydrogen and that where A isunsubstituted phenyl and Y¹ and Y² are both oxygen, then:

-   -   (a) where X is a direct bond, R²-R⁴ together represent other        than either two cyano groups or two halogen atoms when R is        ethyl;    -   (b) where X is —CO(O)—, R²-R⁴ together represent other than one        halogen and one cyano group, and    -   (c) where X is an acetylene group, R²-R⁴ together represent        other than one cyano group and two halogen atoms.

Compounds of formula (I) are compounds which have a high ΔE value, andare therefore particularly useful as dopants which increase the ΔE valueof liquid crystal compounds and particularly nematic mixtures. Certainof the compounds, and in particular those with three rings, maythemselves have liquid crystal properties.

As used herein the term “alkyl” refers to straight or branched chainalkyl groups, suitably containing up to 20, more suitably up to 10 andpreferably up to 6 carbon atoms. The term “alkylene” refers to alkylgroups which are divalent and “cycloalkyl” refers to alkyl groups whichhave at least 3 carbon atoms, and which are cyclic in structure. Theterm “alkenyl” refers to straight or branched unsaturated chains havingfrom 2 to 20 and preferably from 2 to 10 carbon atoms. The term“alkenylene” refers to divalent alkenyl groups. The term “aryl” refersto aromatic rings such as phenyl and naphthyl, but preferably phenyl.

The term “halo” includes fluoro, chloro, bromo or iodo.

Suitable optional substituents for the ring A include halo such asfluoro. Preferably, the ring A is unsubstituted.

Suitably the rings A are six membered rings in particular, phenyl orcyclohexyl. They are preferably joined in a para orientation when thegroups are aromatic, and in an 1,4-orientation when the rings arenon-aromatic. Thus preferred groups A are 1,4-phenylene or1,4-cyclohexyl. Where A is a cycloalkyl ring such as cyclohexyl, theavailable bonds are preferably in a trans relationship as illustrated insub-formula (ii)

In particular, in the compounds of formula (I), A is a 1,4-phenylenegroup.

Where X is a group of sub-formula (i), the compounds of formula (I) havea relatively low viscosity as compared to compounds of formula (I) whichinclude only two rings. However the clearing point of such compoundswould also be higher. Preferably in such compounds X¹ and X² are bothdirect bonds.

Where X is a C₂₋₄alkenylene chain, it is suitably a group of sub-formula(iii), (iv) or (v).

In particular, X is a direct bond, —CO(O)— or acetylene, and mostpreferably is a direct bond or a group —CO(O)—. In particular, X is agroup —C(O)O—.

Thus a preferred sub-group of compounds of formula (I) are compounds offormula (II)

where R¹, Y², n, Y¹, R², R³ and R⁴ are as defined above, X³ is a directbond, —CO(O)—, acetylene, and most preferably a direct bond or a group—CO(O)—. In particular, X³ is a group —C(O)O—.

Suitably R¹ is C₁₋₁₀alkyl, preferably C₁₋₆alkyl, and most preferablyC₁₋₃alkyl such as methyl.

Preferably Y¹ and Y² are oxygen.

Preferably n is 2.

Where R², R³ and/or R⁴ are halo, they are suitably chloro or fluoro andmost preferably fluoro.

Preferably, R³ is other than hydrogen.

In one embodiment, one of R², R³ or R⁴ is cyano.

In a particularly preferred embodiment, R², R³ and R⁴ are all halo andin particular are all fluoro.

Particularly preferred compounds of formula (I) are listed in Table 1below

Compound No. X R² R³ R⁴ 1 bond F CN H 2 bond CN F H 3 bond F F H 4 C(O)OF CN F 5 C(O)O F F F

Compounds of formula (I) can be prepared by methods known in the art.For example, where X is an ester link of formula —C(O)O—, the compoundscan be prepared by reacting an appropriate acid with a phenol. Forinstance these compounds may be prepared by reacting a compound offormula (III) with a compound of formula (IV)

where R¹, R², R³, R⁴, Y¹, Y², A and n are as defined above in relationto formula (I). The reaction is suitably effected in an organic solventsuch as dichloromethane, in the presence of a base and/or a couplingagent. In particular the reaction can be conducted using a combinationof the coupling agent N,N-dicyclohexylcarbodiimide, and a weak base,such as 4-(dimethylamino)pyridine.

Alternatively, the compounds of formula (I) can be prepared by reactinga compound of formula (V)

wherein Y¹, A, X, R², R³ and R⁴ are as defined above in relation toformula (I) with a compound of formula (VI)

wherein R¹, Y² and n are as defined in relation to formula (I) and Z isa leaving group.

The reaction is suitably effected in an organic solvent such as butanoneor tetrahydrofuran in the presence of a base such as an alkali metalcarbonate such as potassium carbonate, and an alkali metal iodide suchas potassium iodide, as well as a strong base such as an alkali metalhydride for instance, sodium hydride. Suitable leaving groups Z includehalo such as chloro, bromo or iodo, mesylate and tosylate, and inparticular are halo groups such as bromo.

Compounds of formula (III), (IV), (V) and (VI) are either knowncompounds or they can be prepared from known compounds by methodsdescribed in the literature.

The liquid crystal compounds of the invention may be used in mixturewith liquid crystal compounds which may or may not comprise compounds offormula (I). Compounds of formula (I) have high ΔE values and may beused as dopants to increase the ΔE values of nematic mixtures. Whenadded to nematic mixtures as dopants, they will lower the thresholdvoltage without destroying the liquid crystalline properties of themixture of increasing its viscosity and hence response time too much.Thus they may be used in a variety of liquid crystal devices includingliquid crystal display (LCD) cells. They may be particularly useful intwisted nematic (TN)-LCDs and supertwist nematic STN-LCDs where lowthreshold voltages and operating voltages are required. Such devicesform a further aspect of the invention.

The invention will now be particularly described by way of example.

EXAMPLE 1

Preparation of Compound 5 in Table 1

Step 1

The Synthesis of 4-(2-methoxyethoxy)benzoic Acid

4-Hydroxybenzoic acid (3.00 g, 2.17×10⁻² mol) was dissolved in a mixtureof ethanol (15 cm³) and potassium hydroxide (3.22 g, 5.64×10⁻² mol) inwater (5 cm³). The solution was then heated gently and stirred before1-bromo-2-methoxyethane (3.32 g, 2.39×10⁻²mol) and potassium iodide(0.01 g, 6.02×10⁻⁵ mol) was added slowly. The resulting reaction mixturewas then refluxed (15 hrs) and the solvent evaporated and the resultingsolid residue dissolved in water (50 cm³). The solution was washed withether and then made strongly acidic with hydrochloric acid. Theresulting precipitate was isolated and recrystallised from ethanol.Yield 1.36 g (32%).

Mpt=154° C.

Step 2

The Synthesis of 3,4,5-trifluorophenyl 4-(2-methoxyethoxy)benzoate(Compound 5 in Table 1)

A solution of 3,4,5-trifluorophenol (0.38 g, 2.55×10⁻³ mol) indichloromethane (10 cm³) was added to a solution ofN,N-dicyclohexylcarbodiimide (0.63 g, 3.06×10⁻³ mol),4-(2-methoxyethoxy)benzoic acid (0.50 g, 2.55×10⁻³ mol),4-(dimethylamino)pyridine (0.03 g 2.55×10⁻⁴mol) in dichloromethane (5cm³), at 0° C. and then left to stirred overnight, filtered to removeprecipitated material (DCU) and the filtrate evaporated down underreduced pressure. The crude product was purified by columnchromatography on silica gel using a 1:1 dichloromethane-petroleum ether(40°-60° C.) mixture as eluent, followed by recrystalisation fromethanol. Yield 0.32 g (38%), GC purity (99.76%).

Mpt=75° C.

Compound 4 in Table 1 was prepared in an analogous manner.

EXAMPLE 2 The Synthesis of 3,4-difluoro-4′-(2-methoxyethoxy)biphenyl(Compound 3 in Table 1)

A mixture of 3,4-difluoro-1,1′-biphenyl-4-ol (0.50 g, 2.43×10⁻³ mol) of1-bromo-2-methoxyethane (0.34 g, 2.43×10⁻³ mol), potassium iodide (0.04g, 2.43×10⁻⁴ mol), potassium carbonate (1.34 g, 9.72×10⁻³ mol) andbutanone (20 cm³) was then heated overnight under reflux. The mixturewas filtered to remove inorganic material and the filtrate evaporateddown under reduced pressure. The crude product was purified by columnchromatography on silica gel using dichloromethane as the eluent andrecrystallisation from hexane to give the pure (GC: 100%) desiredproduct (0.15 g 23%).

Mpt=57° C. CHN: Expected C 68.17%, H 5.34%. Results C 68.01%, H 5.22%.

¹H NMR (CDCl₃) δ₄₀₀: 3.47(3H, s), 3.79(2H, t), 4.17(2H, t), 7.00(2H, dt, J≈8.7 Hz), 7.15-7.26(2H, m), 7.30-7.35(1H, m), 7.44(2H, d t, J≈8.7Hz). IR μ_(max)/cm⁻¹: 3001, 2935, 1608, 1510, 1456, 1266, 1231, 1129,1062, 1033, 925, 862, 820 and 524. MS m/z: 264(M⁺, M¹⁰⁰),233(C₁₄H₁₁F₂O⁺), 206(C₁₂H₇F₂O⁺), 188(C₁₂H₆F₂ ⁺).

EXAMPLE 3 The Synthesis of4-fluoro-4′-(2-methoxyethoxy)biphenyl-3-carbonitrile (Compound No. 2 inTable 1)

A mixture of 4-fluoro-4′-hydroxy-1,1′-biphenyl-3-carbonitrile (0.50 g,2.35×10⁻³ mol), 1-bromo-2-methoxyethane (0.33 g, 2.35×10⁻³ mol),potassium iodide (0.04 g, 2.35×10⁻⁴ mol) and potassium carbonate (1.30g, 9.40×10⁻³ mol) in butanone (20 cm³) was reacted, worked up andpurified as described for compound 3 in Example 2. Yield 0.26 g (40%),GC purity (100%).

Mpt=94° C. ¹H NMR (CDCl₃) δ₄₀₀: 3.44(3H, s), 3.79(2H, t), 4.17(2H, t),7.02(2H, d t, J≈8.5 Hz), 7.23-7.27(1H, m), 7.43(2H, d t, J≈8.5 Hz),7.72-7.76(2H, m). IR ν_(max)/cm⁻¹: 2929, 2239, 1610, 1494, 1450, 1242,1121, 1065, 926, 827 and 533. MS m/z: 271(M⁺, M¹⁰⁰), 240(C₁₅H₁₁OFN⁺),213(C₁₃H₈OFN⁺).

EXAMPLE 4 The Synthesis of3-fluoro-4′-(2-methoxyethoxy)biphenyl-4-carbonitrile (Compound No. 1 inTable 1)

A mixture of 3-fluoro-4′-hydroxy-1,1′-biphenyl-4-carbonitrile (0.50 g,2.35×10⁻³ mol), 1-bromo-2-methoxyethane (0.33 g, 2.35×10⁻³ mol),potassium iodide (0.04 g, 2.35×10⁻⁴ mol) and potassium carbonate (1.30g, 9.40×10⁻³ mol) in butanone (20 cm³) was reacted, worked up andpurified as described for compound 3 in Example 2. Yield 0.40 g (63%),GC purity (99.86%).

Mpt=83° C. CHN: Expected C 70.84%, H 5.20%, N 5.16%. Results C 71.01%, H5.25%, N 5.26%. ¹H NMR (CDCl₃) δ₄₀₀: 3.47(3H, s), 3.79(2H, t), 4.18(2H,t), 7.04(2H, d t, J≈8.5 Hz), 7.41(2H, d quartet, J≈8.2 Hz), 7.52(2H, dt, J≈8.5 Hz), 7.64(1H, d d). IR ν_(max)/cm⁻¹: 2934, 2234, 1614, 1493,1438, 1257, 1123, 1062, 928, 822 and 522. MS m/z: 271(M⁺, M¹⁰⁰),240(C₁₅H₁₁OFN⁺), 213(C₁₃H₈OFN⁺).

EXAMPLE 5

Properties

The transition temperatures in ° C. for the phases of the compounds ofthe invention were tested using conventional methods and equipment. Theresults are summarised in Table 2.

TABLE 2 Compound No Cr I 1 • 83 • 2 • 94 • 3 • 57 • 4 • 72 • 5 • 75 •Dipole Moments

These may be either measured experimentally or calculated usingmolecular modelling techniques. For example the molecular modelleddipole moment μ(D) for Compound No 4 in Table 1 is 8.50 and it wasmeasured as μ 7.63 Debye.

EXAMPLE 6

Liquid Crystal Properties of Mixtures

Compounds of the invention were added to a general liquid crystal hostmixture comprising ethyl linked phenyl cyclohexanes in an amount of 10%and the properties of the mixtures were tested using conventionalmethods.

Clearing Points

These were measured with the results reproduced in Table 3.

TABLE 3 Mixture No. Mixture Clearing point ° C. 1 Host mixture 53.4 2Host mixture + 10% compound No 5 52.1 3 Host mixture + 10% compound No 650.4

Compounds of the invention therefore have the effect of reducing theclearing point of liquid crystal mixtures.

Birefringence Measurements

Refractive indices and birefringence for the mixtures over varioustemperatures were measured and the results are shown in Tables 4 and 5.In these tables, “ne” signifies the extraordinary refractive indices,and “no” the ordinary refractive indices as understood in the art.Measurements were made on an Abbé refractometer.

TABLE 4 Mixture No 2 (see Table No 3) Temperature ° C. ne NoBirefringence 50.91 1.48973 1.5492 0.05946 49.9 1.48896 1.55207 0.0631144.96 1.48663 1.56377 0.07714 39.93 1.48625 1.57101 0.08476 34.981.48615 1.57782 0.09167 29.99 1.48675 1.58253 0.09578 25.06 1.487381.5876 0.10021 20.05 1.48801 1.5914 0.10338 15.06 1.48892 1.595480.10655 10.07 1.48996 1.59933 0.10937

TABLE 5 Mixture No 3 (see Table No 3) Temperature ° C. ne NoBirefringence 48.91 1.49196 1.54367 0.05171 44.95 1.48812 1.555470.06735 39.95 1.48665 1.56604 0.07939 34.98 1.48653 1.57292 0.0863829.97 1.48667 1.57879 0.09212 25.06 1.48725 1.5838 0.09656 20.06 1.48791.58876 0.10085 15.05 1.4888 1.59258 0.10378 10.08 1.48962 1.596270.10665

These results show acceptable birefringence properties for the mixtures.

Switching Behaviour

The switching behaviour the mixtures was measured in a 6 μm cell usingpolyimide 32 alignment. Results are shown in FIGS. 1 and 2, where FIG. 1shows the results with Mixture 2 in Table 3 and FIG. 2 shows the resultswith Mixture 3 in Table 3.

Dielectric Anisotropy

This property of the mixtures defined in Table 3 above were measured andthe results given in Table 6.

TABLE 6 Mixture No Epar εperp Δε 2 13.495 5.513 7.98 3 6.523 1 12.955.13 7.82

1. A compound of formula (I)

where R¹ is alkyl or alkenyl, Y¹ and Y² are independently selected fromoxygen or sulphur, n is an integer of from 1 to 5, A is an optionallysubstituted phenyl or an optionally substituted cycloalkyl ring, X is adirect bond, a C₁₋₄alkylene, a C₂₋₄alkenylene, an acetylene, —CO(O)— ora group of sub-formula (i)

where X¹ and X² are independently selected from a direct bond, aC₁₋₄alkylene, a C₂₋₄alkenylene, an acetylene or —CO(O)— and R², R³ andR⁴ are independently selected from hydrogen, halo or cyano, providedthat no more than one of R², R³ and R⁴ is hydrogen and that where A isunsubstituted phenyl and Y¹ and Y² are both oxygen, then: (a) where X isa direct bond, R²—R⁴ together represent other than either two cyanogroups or two halogen atoms when R¹ is alkyl; (b) where X is —CO(O)—,R²—R⁴ together represent other than one halogen and one cyano group, and(c) where X is an acetylene group, R²—R⁴ together represent other thanone cyano group and two halogen atoms.
 2. A compound according to claim1 wherein the ring A is an unsubstituted six membered ring.
 3. Acompound according to claim 1 wherein the ring A is a 1,4-phenylene or1,4-cyclohexyl.
 4. A compound according to claim 1 wherein X is a groupof sub-formula (i) as defined in claim 1, and X¹ and X² are both directbonds.
 5. A compound according to claim 1 wherein X is a C₂₋₄alkenylenechain of sub-formula (iii), (iv) or (v).


6. A compound according to claim 1 wherein X is a direct bond, —CO(O)—or acetylene.
 7. A compound according to claim 1 wherein R¹ is C₁₋₃alkyl.
 8. A compound according to claim 1 wherein Y¹ and Y² are oxygen.9. A compound according to claim 1 wherein n is
 2. 10. A compoundaccording to claim 1 wherein at least one of R², R³ and/or R⁴ is fluoro.11. A compound according to claim 10 wherein R², R³ and R⁴ are allfluoro.
 12. A compound according to claim 1 wherein R³ is other thanhydrogen.
 13. A compound according to claim 1 wherein one of R², R³ orR⁴ is cyano.
 14. A compound according to claim 1 of formula (II)

where R¹, Y², n, Y¹, R², R³ and R⁴ are as defined in claim 1, and X³ isa direct bond, —CO(O)— or acetylene, subject to the relevant provisosset out in claim
 1. 15. A compound according to claim 14 wherein R¹ isC₁₋₃ alkyl.
 16. A compound according to claim 14 wherein Y¹ and Y² areoxygen.
 17. A compound according to claim 14 wherein n is
 2. 18. Acompound according to claim 14 wherein at least one of R², R³ and/or R⁴is fluoro.
 19. A compound according to claim 18 wherein R², R³ and R⁴are all fluoro.
 20. A compound according to claim 14 wherein R³ is otherthan hydrogen.
 21. A compound according to claim 14 wherein one of R²,R³ or R⁴ is cyano.
 22. A process for preparing a compound of formula (I)as defined in claim 1 wherein X is a group of formula —C(O)O—, theprocess comprising reacting a compound of formula (III) with a compoundof formula (IV)

where R¹, R², R³, R⁴, Y¹, Y², A and n are as defined above in relationto formula (I).
 23. A process for preparing a compound of formula (I) asdefined in claim 1 which process comprises reacting a compound offormula (V)

wherein Y¹, A, X, R², R³ and R⁴ are as defined in claim 1 with acompound of formula (VI)

wherein R¹, Y² and n are as defined in relation to formula (I) and Z isa leaving group.
 24. A liquid crystal mixture comprising a compoundaccording to claim
 1. 25. A compound according to claim 1, wherein thecompound is provided in a liquid crystal device.
 26. A liquid crystalmixture according to claim 24, wherein the liquid crystal mixture isprovided in a liquid crystal device.